Slack adjuster



Oct 10, 1939- lo. RAsMussEN 5r AL 2,175,446

sLAcK ADJusYTER original Filed VMay 28, 193s nventors c/f/zf pasmwsezz Bg 75K/Mft] C Wiki? Patented Oct. 10, 1939 UNITED STATES 2,115,446 sLAox ADJUSTER Olaf Rasmussen and Richard C. Rike, Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original 82,207.

application May 28, 1936, Serial No. Divided and `this application February 14, 1938, Serial No. 190,426

c claims. (c1. iss-'795) This invention relates to brakes, and has been designed to automatically take up excessive clearances between the drum and shoes of a hydraulically operated vehicle brake.

5 l An object of the invention is to provide means to take up excessive clearances by mechanism suitably housed within the so-called wheel cylinder of the hydraulic brake system.

Another object is to provide such an adjustl ment superimposed upon a predetermined lost motion connection in the applying means designed to ensure a necessary degree of shoe clearance.

Other objects comprise `the accomplishment of'A 30 there are shown two shoes 9 and I I normally held from drum Contact by a releasing spring I3.

suitably supported as bythe backing plate or cover for drum 1 is a wheel cylinder I5. Fluid is admitted through an opening I1 to an inter- 35 mediate part of the cylinder by means of a conduit such as I8 (see Figure- 4) from a master cylinder, not shown. At I9 is an air bleed hole which is normally closed by a plug 20 (see Fig. 4) Within the cylinders are pistons 2I and 23 pro- 40 vided with sealing cups 25. Between the pistons there may be a spring 21.

Axial members or plungers 29 have bifurcated heads 3I embracing the webs of shoes 9 and II. Externally each plunger is provided with a helical l ratchet tooth formation 3l). The plungers engage the pistons and the spring i3 functions'to push the plungers and pistons to brake release positionthe position shown. The cylinder ad jacent each end is formed with a shoulder 33 50 engaged by a radially extended part of a pawl retainer 35. The retainer is held against the shoulder by a cover 31 secured by screws or the like 39. A dust guard 4I preferably of rubber is held to the cylinder adjacent an extension 43 of 55 the cover and grips the end oi the shoe. Within the retainer and partly positioned by the cover 31 are a plurality of radially directed pawls 45, their teeth engaging the ratchet device 30. A suitable spring 32 serves to project the pawls into the position shown. It will be noted that ysince 5 the ratchet formation is helical and since the pawls are circumferentially spaced they engage at slightly dierent positions axially of the plunger, this being permitted by the spaced relation cf the walls of the retainer and cover, thereby permitting slightly changed positions of the pawls. Successive ones of the pawls may thus act to grip the plunger and engage the retainer wall a to effect a finer adjustment than would be possibie with a single pawl. 16

The operation of the mechanism is as follows:

' It may be assumed that Figure 1 shows the parts in brake release position. The upper pawl (marked 45a to distinguish it from the other4 marked 45) contacts the retainer wall, its tooth 20 being engaged in the ratchet. It thus limits the release movement of `the shoe and plunger 29. At the same time pawl 45 lies against the cover. 31 and is not holding the plunger from inward movement. The uid entering at I1 moves the 25 piston 2| (and also 23) toward the end of the shoe. The shoe is moved'to contact the drum by means of plunger 29. If 'the lining is not worn appreciably the movement of the plunger will cause the tooth of the lower pawl 45 to slide to- 30 ward but not over the top of the cooperating ratchet tooth. At the same time the tooth of the other pawl remains at the bottom of the ratchet as the pawl moves toward a position corresponding to that shown by 45. It is during this movement of pawl a from the position shown to a position like that oi 45 in Figure 1 that the shoe clearance necessary to accommodate changes in theA drum is taken up. The lining wear may be such that the tooth of pawl 45 jumps over a 40 ratchet tooth. If so, upon the return of the plunger, pawl 45 may move to the right suiliciently to engage the wall of the retainer 35 and hold the plunger. There is thus afforded a xed dimension lost motion to accommodate 45 drum changes, and there is also provided a ner adjustment than would be the case if circular teeth were cut on the plunger or if but a single pawl were used with a helical groove. Obviously more than two pawls may be used if still ner adjustment be needed. Still another advantage results fromv the use of a helical groove. When the lining is replaced it is possible to release plunger 29' from the shoe and, merely by rotating it, to relocate the pawls toward tue bifurcated end of the plunger. It is not necessary to provide any means to lift the pawl as would be the case with a circular groove.

Y By the location within the cylinder'and by means of the protection aiorded by the boot, the self-adjusting expedient is fully protected from foreign matter and manual adjustment is not required throughout the life of the lining.

In Figure 2 is shown a somewhat modified form. In this embodiment the drum and shoe are designated by the same reference characters as are used in Fig. l. 'I'he same piston 2| slides in a slightly modied cylinder |5a. Into the cylinder |5a is inserted a retainer |35 to engage a shoulder |33. A disc |31 closes alchamber within the retainer and th`e assembly is held in position by a nut |39 threaded into the end of the cylinder. The pawls are marked |4| and are projected into engagement with the helical toothed periphery of a sleeve-like ratchet |43.- The end of the ratchet sleeve is bifurcated and embraces the web of the shoe. Reciprocable within ratchet sleeve |43 is a plunger 45 operably engaging the shoe web and having a head |41 to contact with the piston 2|. It will be noted that when both the ratchet and 'the plunger engage the shoe web as they do when the brake is released, the length of the plunger is such that the head. |41 is spaced slightlyfrom the adjacent end |48 of the ratchet sleeve. The pawls act in sequence in determining the release position because of the helical character of the ratchet. The space |50 between the head |41 and the ratchet sleeve is made suflicient to provide a necessary clearance between the drum and shoes. Such a clearance is required to accommodate drum changes such as may be caused by heat or distortion under the influence of pressure.A When the head |41 is moved by the piston the opposite end pushes the shoe and spaces the shoe from the ratchet sleeve. When the head engages and moves the ratchet sleeve the pawls may or may not determine a new retracted position of the shoev dependent upon the condition of the lining. Since the end of the plunger has moved the shoe from contact with the ratchet sleeve, the plunger will return suiiiciently to develop a spaced relation between the shoe and drum, equivalent to the illustrated space between the head 2| and the ratchet sleeve, before the ratchet sleeve engages and stops the release movement of the shoe. Sufficient shoe clearance is thus ensured to accommodate contraction of the drum as it cools and restoration from any distortion which may have been imparted to it in the act of brake application.

The number of the pawls determines the fine` ness of the adjustment for correcting lining wear. This form of the invention is believed to possess v especial merit in `that there is a predetermined spacing between the plunger and ratchet sleeve to accommodate drum changes regardless of the variable position of the ratchet sleeve due to lining lwear.

In Figure 3 is a modification employing the same drum, shoes and piston. Cylinder |5b has a pawl retainer |5| carrying a plurality of -axially spaced pawls |53 projected by springs' |55 into contact with circular ratchet teeth |51 on a ratchet 'sleeve |59. A plate |6| and snap ring |63 position the parts. 'I'he axial spacing of the pawls and the circular (instead of helical) ratchet teeth are to secure the ne adjustment. Figure 4 shows that there may be four of these pawls. Here, as before, .the'spacing of the .head |41 of plunger |45 from the end |52 of the ratchet sleeve |59 is for the purpose of accommodatingv changes in drum contour, the pawl and ratchet functioning solely to accommodate lining wear. In some hydraulic brake wheel cylinders there is used a piston seal secured peripherally to the cylinder, in which cases it is not. expedient that the piston assume new positions of adjustment outward toward the end of the cylinder for changes in lining wear. Figure 5 shows an adaptation of our invention for a wheel cylinder having such a piston seal. In this gure the drum'1 and shoe 9 are like those of the other embodiments. The piston -|65 is advanced by an expansible seal, seal |61 being representative of that type which is anchored to the cylinder instead of slidable with the piston. The seal is secured' peripherallyin the junction of the central part'i 69 of the cylinder and an end part thereof marked |1|. Screw means |13 is shown as securing together parts |1| to |69 and its extended end |15 is received in a notch of the piston |65 to guide the latter. 'I'he piston is provided with pawls |11.projected radially by springs |19 to engage a helical ratchet formation |18 on a plunger |8|. A closure |83 secured by screws |85 positions the pawls. Carried by the plungeris a fixed ring |84 for a purpose to be explained. A disc |86 is held against a shoulder near the end of -part |1|. yby fastening means |89. Between parts |86 and |81 arepawls |9| projected by springs |93 to engage a helical ratchet formation on the outer surface of ratchet sleeve |91. Sleeve 91 is bifurcated to straddle and, in brake release position, to engage the web of shoe 9 along with the head |99 of the plunger |8| which is mounted "to reciprocate through the ratchet sleeve. It

An end closure 61 is secured will be seen that when both the bifurcated end Fluid admitted behind the seal |61 bulges the l. seal to a convex form and the piston |65 is advanced. Since the pawls lock the plunger to the piston for this direction of movement, the plunger |8| is advanced and the shoe is moved to contact the drum. After a limited movement, ring |84 engages the end of the ratchet sleeve |91 and if there has been an appreciable lining wear one of the pawls |9| may jump'over the ratchet tooth and determine a new position of release for the shoe,ratchet sleeve and plunger |8|. It will be clear that changes in drum contour are provided ,for by the always fixed spacing between the inner end of ratchet sleeve |91 and the plunger ring |84. In the event of ratchet adjustment the pist0n |65 would not return to its original position unless added provision be made to this end. In the forms described above, the piston did assume vnew positions. In those cases, however, the seal moves with the piston and since the reservoir could be relied on to supply the additional duid beginning of its movement to initiate the movement of the plunger. It will be understood that this expedient may be used with a conventional seal as in the other gures, but it is of especial use with such seals as those typitled by diaphragm |61 of Figure 5.

This application is led as a division of application Serial Number 82,207, filed on Mary 28, 1936, by the same applicants.

We claim:

1. In brake mechanism, a rotatable member, a shoe adapted to engage the rotatable member and retard its rotation, brake applying means comprising a cylinder, a piston element therein,

. motion transmitting means between said piston4 element and shoe member, said transmitting means including an axially movable member having an external tooth formation, a plurality of pawls carried by the cylinder and spaced cir,

cumferentially, and yielding means pressing said pawls radially toward said externally toothed member, together with a plunger axially slidable through said toothed member, yielding means biasing said piston to a predetermined release position, and pawl and lratchet means between said piston and plunger.

' 2. A brake drum, a shoe to engage the drum, a hydraulic brake cylinder, a piston in said cylinder, a plunger between said piston and shoe, a sleeve surrounding said plunger, said sleeve having ratchet teeth, a plurality oi pawls carried by said cylinder, yielding means to project said pawls into engagement with said ratchet teeth, said plunger having a part movable therewith and adapted to engage said sleeve but spaced from said sleeve in brake release position, whereby said sleeve functions as an adjustable stop and whereby the work end of the plunger projects beyond the sleeve in the act of brake application to ensure predetermined shoe clearance upon brake release, together with a pawl and ratchet device between the piston and plunger to permit return of the piston to a predetermined initial position regardless of sleeve adjustment.

3. A brake drum, a shoe to engage the drum,

a hydraulic brake cylinder, a piston in said cylinder, a plunger between said piston 'andshoe, a sleeve surrounding said plunger, said sleeve having ratchet teeth, a plurality of pawls carried by'said cylinder, yielding means to project said pawls into engagement with said ratchet teeth, said plunger having a part movable therewith and adapted to engage said sleeve but spaced from said sleeve in brake release position, whereby said sleeve functions as an adjustable stop and whereby the work end of the plunger projects beyond the sleeve in the act of brake application to ensure predetermined shoe clearance upon brake release, a diaphragm perlpherally carried by said cylinder and adapted to move said piston, a pawl and ratchet device between the piston and plunger to permit restoration of said piston to the same idle position regardless of sleeve adjustment, and yielding means to restore said piston as aforesaid.

4. A hydraulic brake applying device for a brake shoe comprising a cylinder, a piston therein, a plunger between the piston and shoe, yielding means to restore the plunger to a predetermined release position, and a take-up device between the piston and plunger and including mutually engaging parts carried bysaid piston and plunger to permit the restoration' of the piston, said take-up device rendering said piston operative upon said plunger in positions of relative adjustment between the piston and plunger.

5. A hydraulic brake applying means for vehicles having a drum and a shoe to engage the drum, a brake cylinder, a piston reciprocable within said cylinder, a plunger between the piston and shoe, a one-way take-up device between the piston and plunger, a sleeve surrounding the plunger, and a one-way take-up device between the cylinder and sleeve.

6. The invention deiined by claim 5, means carried by said plunger adapted to engage and move said sleeve after a limited movement of said plunger relative thereto whereby shoe wear is compensated, shoe clearance provided and complete restoration of the piston is eil'ected.

' f OLAF RASMUSSEN. RICHARD C. RIKE. 

